Project Summary: Chronic hypoxic pulmonary hypertension (PHTN) is a major clinical problem, complicating most lung and heart disorders. The development of chronic hypoxic PHTN is a major complication of COPD, adding significantly to the poor prognosis and lethality of COPD. The prevalence of PHTN in COPD is quite large. Patients with COPD develop varying degrees of pulmonary vascular remodeling (a key determinate of PHTN) early in their clinical course. In a disorder as complex as COPD, remodeling requires the participation of several factors, including cigarette smoke, oxidant stress, inflammation, and persistent or intermittent hypoxia. Proliferation of pulmonary artery (PA) smooth muscle cells (SMCs) at the medial/adventitial border is a prominent feature of the structural change. Integral membrane peptidases, found in fairly high abundance in the lung, could play an important role in human pulmonary vascular remodeling. We have shown that one of these peptidases, Neprilysin (NEP), is an important determinatn of susceptability to chronic hypoxic PHTN. NEP null mice have an exaggerated pulmonary hypertensive response to chronic hypoxia, and resident PA SMCs have increased growth compared to their wild type counterparts. Lung NEP expression decreases in response to chronic hypoxia by unknown mechanisms;the decrease in NEP is most striking in distal vessels where early PA SMC proliferation and migration occurs. We will test the Overall Hypothesis that: Decreased NEP vs other peptidases predisposes to the development of increased pulmonary vascular remodeling in COPD. We propose two aims. The first will involve analysis of NEP activity level compared to other peptidases in `normal'and diseased human lung tissue. We will test if change in peptidase activity and/or expression parallel clinical characteristics of COPD severity and pulmonary vascular remodeling (and ultimately PHTN). The second will be to determine the lung structure (vessel vs airway vs alveolar walls), location (proximal vs distal), and cell type (endothelial, smooth muscle, or fibroblast) exhibiting the greatest changes in NEP vs other peptidase expression in closest proximity to the most substantial vascular remodeling using immunohistochemical analyses and laser capture microdissection. These studies may help increase our understanding of mechanisms that control susceptibility to chronic hypoxic PHTN in COPD and could also identify new therapeutic targets to limit or reverse this important clinical problem. (End of Abstract) PUBLIC HEALTH RELEVANCE: Project Narrative: Elevated pressure in the blood vessels in the lung is called pulmonary hypertension. Pulmonary hypertension induced by exposure to low oxygen levels (hypoxia) is a major clinical problem and can be found in many patients with lung and heart disorders;when sustained, it can lead to heart failure. Pulmonary hypertension is a major and common complication of chronic obstructive pulmonary disease (COPD). An important factor in pulmonary hypertension is the abnormal structural change that occurs in the blood vessels. Smooth muscle cells in the wall of lung arteries may grow abnormally in response to hypoxia leading to increased vessel wall thickness and a reduction in the vessel diameter. A protein on the cell surface, Neprilysin, may play an important role in regulating susceptibility to pulmonary hypertension. Mice lacking the Neprilysin protein have increased pulmonary hypertension in response to low oxygen. The smooth muscle cells isolated from these mouse lungs also grow faster than normal cells. We plan to analyze Neprilysin in the lungs of patients with varying degrees of COPD and compare it to other related proteins. We will do this in two specific steps. The first step will involve analysis of Neprilysin and the other proteins in normal and diseased human lung tissue. We will then see if the levels of these proteins change in relation to the severity of the disease and extent of pulmonary vascular structural change (a marker of pulmonary artery hypertension). The second will be to determine the lung structure, location, and cell type that exhibits the greatest amount of change in protein expression. These studies may help increase our understanding of mechanisms that control susceptibility to chronic hypoxic pulmonary hypertension and could also identify new therapeutic targets to limit or reverse this important clinical problem.